README: update text about portal backends

README.md

@@ -356,7 +356,7 @@ To use the portal implementation, add `-DNFD_PORTAL=ON` to the build command.
 
 Unlike Windows and macOS, Linux does not have a file chooser baked into the operating system.  Linux applications that want a file chooser usually link with a library that provides one (such as GTK, as in the Linux screenshot above).  This is a mostly acceptable solution that many applications use, but may make the file chooser look foreign on non-GTK distros.
 
-Flatpak was introduced in 2015, and with it came a standardized interface to open a file chooser.  Applications using this interface did not need to come with a file chooser, and could use the one provided by Flatpak.  This interface became known as the desktop portal, and its use expanded to non-Flatpak applications.  Now, most major desktop Linux distros come with the desktop portal installed, with file choosers that fit the theme of the distro.  Users can also install a different portal backend if desired.  There are currently two known backends: GTK and KDE.  (XFCE does not currently seem to have a portal backend.)
+Flatpak was introduced in 2015, and with it came a standardized interface to open a file chooser.  Applications using this interface did not need to come with a file chooser, and could use the one provided by Flatpak.  This interface became known as the desktop portal, and its use expanded to non-Flatpak applications.  Now, most major desktop Linux distros come with the desktop portal installed, with file choosers that fit the theme of the distro.  Users can also install a different portal backend if desired.  There are currently three known backends with file chooser support: GTK, KDE, and LXQt; Gnome and Xapp backends depending on the GTK one for this functionality.  The Xapp backend has been designed for Cinnamon, MATE or XFCE.  (other desktop environments do not currently seem to have a portal backend.)
 
 ## Platform-specific Quirks